<?php

namespace collections\set;

interface Set
{
    /** @return int */
    public function size();

    /** @return boolean */
    public function isEmpty();

    /** @return boolean */
    public function contains(/* mixed */ $o);

    /** @return array */
    public function toArray();

    /** @return boolean */
    public function add(/* mixed */$e);

    /** @return boolean */
    public function remove(/* mixed */ $e);
}